There are 2 sources I know of that confirm Feierabend and Feyerabend come from the same background. In Paul Feyerabend's autobiography "Killing Time", he says his grandfather changed the family spelling from Feierabend to Feyerabend. At the Univ of Utrecht web site on European printers, the 16th century printer Sigismund (and Hieronymus and Johannes) Feyerabend spelled his names Feierabend, Feirabend, Feyrabend, Feierabent, Feyerabent and more at various times during their lives lives.